1. Field of the Invention
The invention pertains to a mineral fibrous material which serves as an absorbent, especially for hygienic products such as diapers, sanitary napkins, bandages and similar products.
2. Background of the Prior Art
Materials intended for this type of use must satisfy multiple criteria. They must especially possess a satisfactory absorbent capacity.
These materials must also be perfectly innocuous in the intended usage, and, in a more general manner, they must meet all of the requirements for hygienic products, especially those which are utilized in direct contact with the body.
The choice of these materials results from their unique set of considerations, which mainly involves their specific properties for this type of use, but also concerns their relatively low cost.
The latter consideration led recently to the development of the utilization of cellulose fibers produced from wood through the use of paper production techniques. These fibers are prepared in the form of what is termed "fluff", i.e., an interlocking product having a low mass by volume. These are short, irregular fibers which, for this reason, form a material having a low degree of cohesion and, overall, whose mechanical properties are modest, if not poorly suited, for the principally intended use. Especially lacking cohesion, the fluff is normally utilized in combination with other materials. Thus, the fluff serving as an absorbent for diapers is always placed inside a covering which serves as its support.
Moreover, the absorbent capacity of these fluffs is limited, as shown in comparative examples provided below.
Other considerations indicate that the fluff is not entirely satisfactory. Thus, because of the very short fibers of which it is comprised, it possesses a poor resistance to compression, whether in its production or in its use. Once it is compressed, its natural tendency to recover its initial volume is very small, and, as a result, its absorbent capacity is reduced considerably.
In the same manner, sinking under weight in the damp state, which constitutes an important characteristic for the use of these materials, is very great, about 50%.
Measures have been proposed to eliminate this mechanical drawback. This pertains especially to the reinforcement of the fluff by mixing it with other materials. In addition to the fact that it is not always convenient to obtain a perfectly homogeneous satisfactory combination, the formation of these compound materials robs the fluff of the advantage constituted by its low cost.
Moreover, the fluff, in the raw state, has a yellow or brown color, which is undesirable for hygienic products. Bleaching them through the use of traditional techniques, especially in the paper production industry, is possible, but entails additional costs, which are still higher as it is necessary to proceed with a subsequent accelerated neutralization of the residues of the chemical agents which are used.
Synthetic organic products have also been proposed to constitute this type of absorbent material. This pertains especially to grafted cellulose fiber-based products. Their absorbent capacity is normally very high, but, due to their high production cost, their uses are restricted.
This also pertains to compound products comprising a fibrous support in which particles or powders of products, which are of various natures, but which present a particularly high degree of absorbency, are dispersed. In addition to their high cost, these absorbent products contribute no mechanical qualities to the overall product. Moreover, their absorbent properties can be limited in use by their tendency to form clusters.
Mineral fiber felts have already been proposed as absorbent materials, especially as a means to fight marine pollution due to hydrocarbons. Other industrial applications also call directly or indirectly on the absorbent properties of the mineral fiber felts, especially glass fiber felts.
In these applications, the felts chosen due to their cost are the type which normally serve in areas in which production is more abundant, namely, that of the felts intended for insulation. Because of the characteristics required for these uses, combined with the production cost imperatives, these products cannot be utilized for physical hygiene.
Specifically, in the most widespread commercial products, the dimensional characteristics of the fibers and notably the presence of fibers having a diameter of about 10 micrometers or more, even in small proportions, causes irritations in contact with the skin which makes them inappropriate for this purpose.
Long, fine and highly regular mineral fibers are also known and produced for highly specialized applications. These fibers are normally produced using techniques known as "flame drawing".
In accordance with these techniques, primary solid filaments having a diameter of about one millimeter are introduced into a high-speed, high-temperature gaseous current. Under the action of this current, the filaments soften and are drawn into fine fibers which, under certain conditions, can be practically continuous. The felts made of these very fine fibers present the advantage of offering excellent insulating properties for very low masses, but the production technique is highly energy-intensive. For these reasons, their main uses are limited to specialized areas, for example, in the aeronautics industry, in which the questions of weight constitute a fundamental element of assessment and in which cost has a lower priority.
Be this as it may, in this utilization, the absorbent aspect of these felts does not appear. Quite on the contrary, attempts are made to preserve the hydrophobic properties as much as possible by adding special lubricants, for example, silicone products.